1. Field of the Invention
The present invention relates to a plasma display apparatus, and more particularly, to a plasma display apparatus for preventing Electromagnetic Interference (EMI).
2. Background of the Related Art
In general, a plasma display apparatus comprises a plasma display panel having a front panel and a rear panel. A barrier rib formed between the front panel and the rear panel forms one unit cell. Each cell is filled with an inert gas containing a primary discharge gas, such as neon (Ne), helium (He) or a mixed gas of Ne+He, and a small amount of xenon (Xe) . If the inert gas is discharged with a high frequency voltage, vacuum ultraviolet rays are generated. Phosphors formed between the barrier ribs are excited to implement images. The plasma display panel can be made thin, and has thus been in the spotlight as the next-generation display devices.
FIG. 1 illustrates a method of implementing gray levels of an image in a plasma display panel in the related art.
As shown in FIG. 1, to represent gray levels of an image of the plasma display panel in the related art, one frame is divided into several sub-fields having a different number of emissions. Each sub-field is divided into a reset period (RPD) for initializing the entire cells, an address period (APD) for selecting a cell to be discharged, and a sustain period (SPD) for implementing gray levels depending on the number of discharges. The sustain period is increased in the ratio of 2n (where n=0, 1, 2, 3, 4, 5, 6, 7) in each sub-field. Since the sustain period is varied every sub-field as described above, gray levels of an image are represented by controlling the sustain period of each sub-field, i.e., a sustain discharge number.
FIG. 2 illustrates a driving waveform of a plasma display apparatus in the related art.
Referring to FIG. 2, each of sub-fields (SF) comprises a reset period (RP) for initializing discharge cells of the entire screen, an address period (AP) for selecting discharge cells, and a sustain period (SP) for sustaining the discharge of selected discharge cells.
In a set-up period (SU) of the reset period (RP), a ramp-up waveform (PR) is applied to the entire scan electrodes Y at the same time. A weak discharge (a set-up discharge) is generated within cells of the entire screen by the ramp-up waveform (PR), thus generating wall charges within the cells. In the set-up period (SD) of the reset period (RP), a ramp-down waveform (NR), which falls from a positive (+) sustain voltage (Vs) lower than a peak voltage of the ramp-up waveform (PR) to a negative scan voltage (−Vy) at a predetermined slant, is applied to the scan electrodes Y at the same time. The ramp-down waveform (NR) generates a weak erase discharge within the cells to erase wall charges generated by the set-up discharge and unnecessary charges of spatial charges, thus allowing wall charges necessary for an address discharge to uniformly remain within the cells of the entire screen.
In the address period (AP), while a negative (−) scan pulse (SCNP) is sequentially applied to the scan electrodes Y, a positive (+) data pulse (DP) is applied to address electrodes X. As a voltage difference between the scan pulse (SCNP) and the data pulse (DP) and a wall voltage generated in the reset period (RP) are added, an address discharge is generated within cells to which the data pulse (DP) is applied. Wall charges are generated within cells selected by an address discharge.
Meanwhile, during the set-up period (SD) and the address period (AP), a positive (+) sustain voltage (Vs) is applied to sustain electrodes Z.
In the sustain period (SP), a sustain pulse (SUSP) is alternately applied to the scan electrodes Y and the sustain electrodes Z. Therefore, a sustain discharge is generated in a surface discharge form between the scan electrodes Y and the sustain electrodes Z in cells selected by the address discharge whenever the sustain pulse (SUSP) is applied as the wall voltage within the cells and the sustain pulse (SUSP) are added. The sustain pulse (SUSP) has the same voltage value as the sustain voltage (Vs).
Meanwhile, in the related art plasma display apparatus, as the driving waveform is applied, EMI is generated toward the font of the plasma display panel.
More particularly, a pulse of a high frequency and a high voltage is applied to the scan electrodes in each of the set-up period, the address period and the sustain period. Therefore, a problem arises because a great amount of EMI is generated in the front of the plasma display panel due to the peaking component of the high frequency current of the pulse.